Convert string to float error in pandas machine learning

Question

For my machine learning code, I have some unknown values with '?' in my csv file. So, I am trying to replace them with 'Nan' but it throws some error. The following code is for the replacement of '?' that I have used. Can anyone please solve this? Thanks in advance !

 import numpy
    import pandas as pd
    import matplotlib as plot
    import numpy as np
    df = pd.read_csv('cdk.csv')
    x=df.iloc[:,0:24].values
    y=df.iloc[:,24].values
    from sklearn.preprocessing import Imputer
    imputer = Imputer(missing_values='NaN', strategy='most_frequent', axis =0,copy=False)
    imputer = imputer.fit(x[:,0:5])
    imputer.fit_transform(x[:,0:5])

    imputer = Imputer(missing_values='normal', strategy='mode', axis =0,copy=False)
    imputer = imputer.fit(x[:,5:7])
    imputer.fit_transform(x[:,5:7])

This is what error it throws,

Traceback (most recent call last):
  File "kidney.py", line 10, in <module>
    imputer = imputer.fit(x[:,0:5])
  File "C:\Users\YAASHI\AppData\Local\Programs\Python\Python36\lib\site-packages\sklearn\preprocessing\imputation.py", line 155, in fit
    force_all_finite=False)
  File "C:\Users\YAASHI\AppData\Local\Programs\Python\Python36\lib\site-packages\sklearn\utils\validation.py", line 433, in check_array
    array = np.array(array, dtype=dtype, order=order, copy=copy)
ValueError: could not convert string to float: '?'

Link for the csv file

This is a common ValueError. It has nothing to do with machine learning, so please do not tag as such — user3483203
– user3483203, Commented Aug 26, 2018 at 2:37
You say you are trying to replace ? with NaN, but you have showed no code which mentions ?. Where is your code to replace the ?s? — John Zwinck
– John Zwinck, Commented Aug 26, 2018 at 2:38

John Zwinck · Accepted Answer · 2018-08-26 02:39:54Z

2

If you want to replace all ? strings with NaN, do this:

df.replace('?', np.nan, inplace=True)

Or better yet, load them as NaN as you read the CSV:

df = pd.read_csv('cdk.csv', na_values=['?'])

answered Aug 26, 2018 at 2:39

John Zwinck

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